1. Field of the Invention
The present invention relates to a gear shifting mechanism of an axle drive system, which is applicable to various industrial vehicles, such as trucks, agricultural tractors, riding mowers and construction equipments. The gear shifting mechanism is used for changing forward and backward traveling direction of a vehicle, or for changing a traveling speed level of a vehicle.
2. Related Art
There is a conventional axle drive system for various industrial vehicles, such as trucks, agricultural tractors, riding mowers and construction equipments, as disclosed in U.S. Pat. No. 5,366,040 and Japanese Patent No. 2,747,803. The conventional axle drive system includes a gear shifting mechanism having an axially slidable slider between axially opposite gears (any of them may be a sprocket). The slider and the opposite gears are provided with respective clutch teeth facing one another so that the clutch teeth of the slider selectively engage with the clutch teeth of one of the opposite clutch gears. The slider integrally movably engages with a shifter. As shown in the document '040, the shifter may have a shifter pawl fitted into a peripheral groove of the slider. The shifter is axially slidable on a fixed shifter shaft and interlockingly connected to a gear shifting manipulator (such as a lever) through a linkage including a rotary shaft, or alternatively, the shifter is fixed onto an axially slidable shifter shaft interlockingly connected to a gear shifting manipulator (such as a lever) through a linkage including a rotary shaft. Anyway, by manipulation of the manipulator, the rotary shaft is rotated, and the rotation is converted to axial movement of the shifter or the shifter shaft, thereby axially sliding the slider so as to engage with one of the opposite clutch gears.
If the conventional axle drive system is provided with a belt type stepless transmission which does not function as a reverser, as disclosed in the document '040, the gear shifting mechanism is disposed on the downstream of the belt type transmission, and a forward traveling clutch gear and a backward traveling sprocket serve as the opposite clutch gears. The slider selectively engages with either the forward traveling clutch gear and the backward traveling sprocket so as to switch forward/backward rotary direction of an axle.
If the conventional axle drive system is provided with a hydrostatic stepless transmission (hereinafter, referred to as “HST”) which can function as a reverser, as disclosed in the document '803, the gear shifting mechanism is provided for expanding the speed changing range of the HST. The opposite clutch gears provide at least two (high and low) rotary speed stages of an axle.
FIG. 13(a) illustrates a part of a gear shifting mechanism constructed as the above (whether it may be provided for switching the traveling direction of a vehicle or the traveling speed stage of a vehicle). The gear shifting mechanism comprises opposite clutch gears 13A and 14A, a slider 16A disposed between the opposite clutch gears 13A and 14A, and a shifter 38A engaging with the slider 16A.
FIG. 13(b) illustrates clutch teeth 113a, 114a and 116a of respective opposite clutch gears 13A and 14A (forward and backward traveling clutch gears, or low and high speed clutch gears). The clutch teeth 113a, 114a and 116a are formed with chamfers 113b, 114b and 116b at ends thereof facing one another. Especially, each of the clutch teeth 116a of the slider 16A has the chamfers 116b on its opposite ends.
However, when the gear shifting operation is performed during traveling of a vehicle, the clutch teeth to engage with each other may collide with each other so as to be flipped out because rotation phases of the clutch teeth to engage with each other do not always agree with each other. In other words, the flipping is continued until the rotation phases agree with each other.
The flipping of the clutch teeth is transmitted from the gear shifting slider to the gear shifting manipulator through the shifter and the linkage, thereby discomforting an operator. Furthermore, the flipping damages the chamfers.
It is understood that the chamfers cause the flipping by themselves. In this regard, since the chamfers facilitate the mutually facing clutch teeth to engage with each other, the clutch teeth on one side enter the tooth spaces on the other side even if the rotation phases do not agree with each other, whereby the clutch teeth are flipped back.
If the end surfaces of the clutch teeth are formed to be flat so as to prevent the flipping, the clutch teeth must engage strictly at the moment the rotation phases agree with each other. However, an operator cannot recognize the moment of the agreement of the rotation phases, and cannot operate the gear shifting manipulator just at the moment of the agreement of the rotation phases.
Therefore, the operation of the gear shifting manipulator may be stopped on the way of its stroke because the flat end surfaces of the clutch teeth, whose rotation phases do not agree, abut against each other. In such a case, an operator may apply excessive force so as to squeeze the clutch teeth into the tooth spaces. When such an excessive force is applied, the clutch teeth may engage with each other suddenly just at the moment of the agreement of the rotation phases, so as to generate such a big shock as to damage the drive system.